Dynamics in one-dimensional spin chains newly elucidated
The data from neutron scattering (left) provide information about absorbed energies in reciprocal space. With the new evaluation, it has been possible to obtain statements about new magnetic states and their temporal development in real space (right). The colours blue and red indicate the two opposite spin directions. © HZB
Neutron scattering is considered the method of choice for investigating magnetic structures and excitations in quantum materials. Now, for the first time, the evaluation of measurement data from the 2000s with new methods has provided much deeper insights into a model system – the 1D Heisenberg spin chains. A new toolbox is available for elucidating future quantum materials has been achieved.
Potassium copper fluoride KCuF3 is considered the simplest model material realising the so-called Heisenberg quantum spin chain: The spins interact with their neighbours antiferromagnetically along a single direction (one-dimensional), governed by the laws of quantum physics.
"We carried out the measurements on this simple model material at the ISIS spallation neutron source some time ago when I was a postdoc, and we published our results in 2005, 2013 and again in 2021 comparing to new theories each time they became available," says Prof. Bella Lake, who heads the HZB-Institute Quantum Phenomena in Novel Materials. Now with new and extended methods, a team led by Prof. Alan Tennant and Dr Allen Scheie have succeeded to gain significantly deeper insights into the interactions between the spins and their spatial and temporal evolution.
Dynamics like a wake
"With neutron scattering, you sort of nudge a spin so that it flips. This creates a dynamic, like a wake when a ship is sailing through water, which can affect its neighbours and their neighbours," Tennant explains.
”Neutron scattering data is measured as a function of energy and wavevector” says Scheie “ Our breakthrough was to map the spatial and temporal development of the spins using mathematical methods such as a back-Fourier transformation.” Combined with other theoretical methods, the physicists gathered information about interactions between the spin states and their duration and range, as well as insights into the so-called quantum coherence.
New tool box
The work demonstrates a new tool box for the analysis of neutron scattering data and might foster a deeper understanding of quantum materials that are relevant for technological use.
- Disorder creates new properties in compound semiconductorsAn international research team has demonstrated that the intrinsic disorder of the compound semiconductor CuInSnS₄ can be exploited to influence its optical properties. While the atomic vibrations also sense the local disorder, their response is averaged over many different local environments and therefore appear isotropic, as expected for a cubic crystal. In contrast, the optical excitations, known as excitons, are much more sensitive to the local arrangement of atoms. Surprisingly, they show a direction-dependent optical response even though the average crystal structure is cubic. These findings shed new light on the relationship between disorder and material properties, opening up new options for targeted 'disorder engineering' in optoelectronic and photocatalytic devices.
- Superconducting TES array X-ray spectrometer goes into operation at BESSY IIEurope's first and only TES-spectrometer at a synchrotron source is now in operation at BESSY II, developed within a collaboration between the HZB, the MPI-CEC (Mühlheim-an-der-Ruhr, Germany) and the NIST (Boulder CO, USA). The photon detection efficiency of the new instrument exceeds that of wavelength-dispersive X-ray emission spectrometers by a factor of 100 to 1000. It will be used to investigate the electronic properties of atomically thin layers, nanostructures and highly diluted atomic and molecular samples. The team is looking forward to receiving exciting research proposals from the user community.
- A New Era in Catalysis: ASCEND Launch in Berlin, €30 Million in FundingOn 11 June 2026, the Helmholtz-Zentrum Berlin (HZB) in Adlershof hosted the launch of ASCEND (Accelerated Solutions for Catalysis using Emerging Nanotechnology and Digital Innovation). The event took place in the presence of the Minister of Research, Dorothee Bär, President of the Helmholtz Association, Prof. Dr. Martin Keller, and President of the Max Planck Society, Prof. Dr. Patrick Cramer. Bringing together leading partners from industry and research, ASCEND is supported by BMFTR with €30 million in funding and officially started on 1 April 2026. The initiative aims to accelerate the discovery of next-generation catalysts and enable more sustainable chemical processes.